This study assesses the effects of brain-derived neurotrophic factor (BDNF) on transit through the gastrointestinal tract and on stool frequency and form in normal healthy human volunteers. BDNF is found in very small quantities in the brain, nerve, muscle, and gland cells of humans. Neurotrophic factors are proteins that have been shown in laboratory animals to promote healing and survival of nerve cells. BDNF has previously been studied in over 1,400 patients as a potential treatment for certain neurological diseases. This study evaluates its effects on digestive functions in detail.